Mycotoxins are chemicals produced by fungi (molds) under certain conditions. They are not essential for fungal growth or reproduction, and they are toxic to animals or humans. They are naturally occurring chemicals found in grains, food and feed consumed by humans and animals that cannot be completely avoided. Accordingly, we try to control the amount of such chemicals ingested by humans and animals.

Mycotoxins commonly found in grains or feeds used in Nebraska are aflatoxins, ergot alkaloids, fumonisins, vomitoxin and zearalenone. Information about their
health effects, diagnosis, and treatment may be found
in NebGuide G1513, Understanding Fungal (Mold)
Toxins (Mycotoxins). Information about sampling and analyzing grains or feed for mycotoxins may be found in NebGuide G1515, Sampling and Analyzing Feed for Fungal (Mold) Toxins (Mycotoxins).

Use of Mycotoxin-Contaminated Feeds

It is always safest not to use mycotoxin-contaminated or moldy feed. Even if no detectable amounts of known mycotoxins are present in such feed, unknown or uncharacterized mycotoxins may be present which cannot be detected using existing analytical methods. If mycotoxin-contaminated or moldy feed must be used, feed it to animals that are less sensitive to potential adverse health effects of mycotoxins.

There are many different kinds of mycotoxins belonging to many different classes of chemicals. It is difficult, if not impossible, to generalize about the sensitivity of dif?ferent species to adverse health effects caused by
ingestion? of mycotoxins. But ruminants are generally
among the least sensitive to mycotoxins.

U.S. Food and Drug Administration (FDA) can establish limitations for concentrations of mycotoxins in animal and human foods. Limitations are labeled using different terms, including “action levels” for aflatoxins, “guidance levels” for fumonisins, and “advisory levels” for vomitoxin. USDA Federal Grain Inspection Service has set standards defining ergoty barley, mixed grains, oats, rye, triticale and wheat. The legalities of such designations and their application to animal production are beyond the scope of this NebGuide. The authors recommend that grain, feed and animal producers adhere to those limitations as much as possible.

Limitations placed on mycotoxins in feed are listed in Table I. If federal agencies have not established limitations for a mycotoxin, then we have listed recommendations for limitations found in a published reference. References are listed for all mycotoxins included in the table.

Blending Feeds to Reduce Mycotoxin Concentrations

Blending contaminated feed with uncontaminated feed to reduce mycotoxin concentrations is regulated by federal agencies. Blending food or feed containing a substance in excess of a limitation established by a federal agency may not be permitted. Blending aflatoxin-contaminated commodities is not permitted. The final product produced by blending may be unlawful, regardless of the concentration of the mycotoxin attained by blending.

Under certain circumstances, U.S. FDA may not object to blending feeds containing mycotoxins at concentrations higher than a limitation. In the case of aflatoxin in Nebraska corn harvested in 2002, the State Department of Agriculture requested permission from the U.S. FDA to blend corn containing aflatoxin under certain circumstances. Limitations were placed on uses for the blended products, however. Limitations applied to feed blended for marketing or for use by the grain producer. Before you blend mycotoxin-contaminated feed, contact the State Department of Agriculture for additional information.

If mycotoxin-contaminated feed is to be blended, then mycotoxin content of the uncontaminated and contaminated feeds must be known. Hopefully, the content of the uncontaminated feed will be very low. The following formula can be used to calculate the percentage of contaminated feed in the blended feed to achieve a specific mycotoxin concentration:

F = 100 x (C - L)/(H - L)

where F = fraction of contaminated feed in the final blend expressed as a percentage, C = desired mycotoxin concentration in the final blend, L = mycotoxin concentration in the “uncontaminated” feed, H = mycotoxin concentration in the contaminated feed. H must be greater than L.

For example, say corn was available contaminated with zearalenone at 10 ppm and is to be mixed with corn containing no detectable amount of zearalenone (detection limit 0.5 ppm) to a concentration of no more than 1 ppm. Using the formula to calculate F: C = 1 ppm, L = 0.5 ppm (safer to use the detection limit concentration than to assume there is no zearalenone in the uncontaminated corn), H = 10 ppm. Plugging the numbers into the equation and performing the calculations:

F = 100 x (1 - 0.5)/(10 - 0.5) = 100 x (0.5/9.50) = 5.26%

Since we want the blended grain to contain no more than 1 ppm, it would be better to round F down to 5 percent, so the blended grain should not contain more than 5 percent contaminated corn.